The present invention relates to a method of obtaining a thread running signal in which at least one sensor is attached to the mounting of a thread guide and delivers a signal which, among other things, reflects the oscillations induced in the thread guide by the thread movement.
A method and a thread sensor of this kind are already known from German patent publication DE-OS 29 19 836.
It is the aim in the textile machine industry to be able to monitor the production at each spindle of a spinning machine. A thread break at a spinning position results in a loss of production and paid work and can, in certain cases, also lead to damage to the machine. The main causes of thread breaks are for example thin locations in the yarn, poorly serviced parts in the yarn forming process or incorrect adjustment of the spinning machine.
Known thread monitoring devices detect among other things parameters such as the ballooning of the thread or the speed of rotation of the ring traveller in the ring spinning machine, the temporal changes of the thickness of the running thread or the cross-section of the thread. As a result of the high manufacturing costs such devices are, however, only used in a few machines. The initially named DE-OS 29 19 836 discloses a thread breakage sensor which consists of a piezoelectric element mounted on a part of the thread guide with its output signal being further processed to determine whether a thread break is present.
Through the contact of the thread guide with the spun thread high frequency oscillations of the thread guide arise which are mixed with mechanical oscillations of the ring spinning machine.
As can be seen in DE-OS 29 19 836 the frequency of the mechanical oscillations amounts to about 1 kHz while the thread guide oscillates at about 15 kHz. These latter oscillations are evaluated in DE-OS 29 19 836 to determine whether thread breaks are present in such a way that one discriminates the natural oscillations relative to the mechanical oscillations. Stating more precisely the two connection lines of the piezoelectric element are connected to a bandpass filter which picks up the natural oscillation components in the output signals of the piezoelectric element, i.e. transmits them. These natural oscillation components are then amplified by means of an amplifier to a specific value. A rectifier converts the AC voltage signals into DC voltage signals. A voltage range in which normal operation is guaranteed is determined with the aid of a voltage comparator and a corresponding logic output signal is then present at the output of the comparator (DE-OS 29 19 836, page 10, line 29 to page 11, line 6).
The thread sensor of DE-OS 29 19 836 is however only able to determine thread breaks but is not, however, able to measure thread tension.